It is common in traffic control to use pavement markings for directing vehicles. Typically, solid lines or skip lines are formed on the surface of pavement to guide the drivers of vehicles in safe traffic flow arrangements.
In order to make the pavement striping more visible in darkness, reflective beads have been added to the striping. In wet night time conditions the reflectivity of the road striping is substantially reduced because of the presence of water on the road striping. The water tends to block the light from engaging and being reflected from the beads, making the road conditions hazardous. This hazardous condition may be aggravated because the drivers may be used to having adequate reflection of the headlights for directing the drivers in the proper lanes.
It is known that incorporating vertical surfaces in pavement markings improves the visibility of the marking and the reflex reflectivity of the marking, particularly in wet atmospheric conditions. Regular flat striping is hard to see when wet for several reasons. For example, when 30 meter geometry is applied, where the vehicle lights are 30 meters away from the reflective surface, Schnell's laws of defraction and Fresnell's laws of reflection dictate that about 85% of the light from the headlights is reflected off the surface of the water and does not even reach the reflective striping. Also, of the 15% of the light that is refracted into the water and reflected back, only 28% will be refracted back into the air. If the line was a perfect reflector, only about 4% of the original light would make it back to the eyes of the driver of the vehicle. By incorporating a vertical surface within the line, over 98% of the light is transmitted to the vertical reflecting surface, and 98% of the reflected light refracts back into the air.
The vertical profiles have been achieved by imprinting protrusions in the baseline marking before the base line material has been cured, or by adding the protrusions to the baseline marking before it has cured. Also, reflective protrusions have been developed by coating a core product with adhesive and subsequently dunking the core product in molten glass, or mixing the coated core product in small spherical glass beads. Another example is disclosed in U.S. Pat. No. 6,326,053 in which protuberances are formed in the base line marking and optical elements are partially embedded in the protuberances.
The beads that are used to reflect light may be translucent and therefore retro-reflective, or the beads may be formed of reflective material. This is effective particularly when the beads are elevated above the pavement surface so that they are not submerged in wet conditions.
The pavement markings can be formed in patterns that have some significance to the vehicle operators, such as different formations of striping and skip lines. The arrangement of the striping in the lane of the vehicle may be formed so that when the wheels roll over the striping the wheels tend to vibrate or “rumble”, or the striping may be formed so as to direct the driver of the vehicle with arrows or other direction symbols.
One of the problems of the prior art elevated reflective striping is that the materials of the striping wear away over time due to environmental conditions and particularly due to engagement by the wheels of vehicles on the striping. The reflective beads tend to become loose and eventually separated from the striping, thereby diminishing the amount of reflection provided by the striping. Even when the reflective beads are partially embedded in the striping, the beads tend to become loose and separate from the striping.
Other markings that have a renewable reflective structure tend to have a period of poor reflectivity between the time when the reflective surface has been damaged or lost and other beads have not yet been properly exposed. And the processes for making the reflective markings as described above are expensive.
Thus, this invention addresses the problems of the prior art described above and provides improved reflective pellets for reflective marking of highways, the process of making the pellets, and highway striping that includes the pellets.